Collector motor speed stabilizer. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Collector motor speed stabilizer. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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Collector motors with independent excitation are widely used in electric drives of various mechanisms. They create a significant torque, while allowing you to change the shaft speed from zero to maximum operating speed. The author of the proposed article succeeded in making a relatively simple device for manually adjusting the rotational speed of such an electric motor, automatically maintaining it constant with changes in the supply voltage and mechanical load on the shaft.

Control devices for collector electric motors with independent excitation fall into two main groups: pulse-width and phase controllers. The latter proved to be more reliable. However, industrial products of this type are built according to too cumbersome schemes. The analysis showed that they can be significantly simplified without compromising technical characteristics. The proposed stabilizer and speed controller are designed for KPA-563, KPK-564 and similar engines with a power of 90 ... 120 W at a supply voltage of up to 42 V.

The diagram of the device is shown in the figure.

(click to enlarge)

A pulsating voltage is applied to the M1 electric motor, obtained using a diode bridge VD1 - VD4 from an alternating 36 ... 42 V. The VD6C2 circuit turns the pulsating voltage into a constant voltage, which is fed to the DA9 microcircuit through a voltage stabilizer on the VD1 zener diode and transistor VT1. The HL1 LED serves as a power-on indicator.

From the zener diode VD10, exemplary voltage is removed for stabilization and regulation circuits. The required speed is set by a variable resistor R12, which changes the voltage that is applied to the non-inverting input of the op-amp DA1 through the R15C5R16 filter. Here it is summed with the current feedback voltage. The latter is removed from the resistor R3, connected in series to the motor armature circuit M1, and fed to the input of the op-amp through a voltage divider R5R8 and a filter R3C4R13. Elements R6, VD7, VD8 limit the current feedback voltage during motor overloads.

At the inverting input of op amp DA1, the reference voltage supplied through resistors R19 and R20 is summed with the voltage that is removed from the armature of the motor M1 and fed to the op amp through resistors R14, R21, R22.

Op-amp DA1 is connected according to the scheme of an integrating amplifier, the transmission coefficient and time constant of which determine the characteristics of the stabilization system as a whole. The output voltage of the op-amp controls the pulse shaper on the unijunction transistor VT2. The opening angle of the trinistor VS1 and the average value of the current flowing through the armature winding of the motor M1 depend on their duration. Optocoupler U1 isolates control circuits from power circuits.

The device used capacitors C1 - MBGO or MBGCH, C2, C4, C5, C9 - K50-35, C7, C10 - series K73, C3, C6, C8 - small-sized ceramic; resistors R2 - C5-16, R15, R19, R22 - SP5-2, R12 - PPB-1V, the rest - MLT. When replacing KR140UD1B with another op-amp, for example, K140UD6, one should take into account their differences in the purpose of the conclusions and parameters of the correction circuits

To adjust the stabilizer, an adjustable AC voltage source of 36 ... 42 V is required. In addition, it is necessary to be able to control the speed of the motor shaft when the mechanical load on it changes.

A simple and convenient speed sensor is a conventional microphone head mounted at a distance of a few millimeters from a shaft in which a small permanent magnet is fixed. The pulses introduced into the head winding can be observed on the oscilloscope screen, and their frequency can be measured with a frequency meter. A variable mechanical load on the shaft is created by pressing a piece of dense rubber against it. This method is suitable for motors up to 200 W.

Starting to establish, instead of a constant resistor R5, a tuning resistor with a nominal value of 470 Ohms is installed. The engine of the variable resistor R12 is transferred to the position corresponding to the minimum resistance. Turning on the power, trimming resistor R19 achieve a complete stop of the engine. Then, with a trimming resistor R15, the engine is forced to start rotating at a minimum speed.

After that, the engine of the variable resistor R12 is set to the middle position and, after waiting for the engine to accelerate to a constant speed, its shaft is mechanically loaded. By changing the resistance of the resistor R5, a minimum dependence of the speed on the load is achieved. Now the tuning resistor can be replaced with a constant of the desired resistance.

The tuning resistor R22 is set to a position in which the engine speed remains practically constant when the supply voltage changes by 10 ... 20%. Then the resistance of the resistor R12 is again reduced to a minimum and the tuning resistor R19 sets the rotational speed equal to the lower limit of the specified control interval. This completes the stabilization of the stabilizer.

Author: V.Tushnov, Lugansk, Ukraine

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